one little baby bird

[verity]

Hi, can anyone offer me any help, I live in Adelaide, South Australia and I only got my birds in June so am new to the world of IRNs. I had 4 hatch almost a month ago now and they seem to be going well but one is very small and has no sign of feathers yet and the other 3 are about twice the size and have started to get there feathers. Should I just leave them be and hope for the best? My other question is it has been rather warm (27 - 32 degrees) here for the last few days and it seems very hot in the nesting box, I opened the lid a bit today but the birds shut it, once again should I just hope for the best? Any advice would be great, thanks.